The safety factor for a pressure vessel being what it is, especially considering the heat of steam and its expansive nature when released from confinement, the tendency is to over build a boiler. Steel IMO, has more drawbacks as a boiler than copper. A poor weld in a steel boiler will 'worm' corrode as an unseen eventual failure and the same could be said about a welded copper boiler - but - exclude the risk of corrosion failure in the future with copper. A properly made copper boiler stored for 50 years would be much more reliable that a steel boiler stored for the same period.

I intend to weld together a copper boiler for this mogul and if I survive its use in steaming, I'll write a bit here about how it was done. Although there are 'old hats' here who have been there - done that - there is little text about it. This write-up on coppersmithing a copper boiler is very welcomed and is also an enticement to continue with this copper boiler in lieu of steel. The original desire for copper must have come from reading all that British text and ventures in live steam locomotives when I was a kid. BTW: we just bought a couple of British made injectors that look fine but will be tested in the next week or so - the merryweather boiler (copper) is just about complete. Hoping for the best.
BC

Suppose that the inner portion is made of a copper liner for corrosion resistance and then supported by a steel hull for the pressure and stress support. As far as size my poor understanding of boilers is that they primarily control the longevity of a run and the buildup of power so to me a larger size would be the volume of the tank capacity for water. I guess if I had a end goal for a project it would be to make a steam generator or small go kart.

The company I retired from designed and made copper heat exchanges for industrial use ranging in length up to 4 feet long and 1 1/2 feet in diameter. They were mounted in fixtures and furnace brazed. It was an expensive process so we tried welding for the larger sizes. My reference here is over 30 years old so you have to take it with appropriate consideration. Standard commercial grade copper was 99% pure with up to .1% oxygen. Tests were done using manual welding processes and TIG being the preferred method. We found that the oxygen oxidized the weld from the inside out and reduced weld strength as much as 60%. We were able to eliminate the problem by using deoxidized copper, but, the cost went up 35% eliminating the welding cost advantage over furnace brazing. Possibly today's materials and processes eliminate the oxygen problem. However, it should be considered.

Copper has four attributes that make it very desirable for model boilers. 1. In normal maintained circumstances it will not corrode. 2. It is not prone to embitterment. 3. It is extremely malleable and can stand over 50% elongation before ultimate failure. 4. Has 8 times the thermal conductivity of steel.

Copper also has some draw backs. 1. It's thermal expansion is 50% greater than steel. 2. It begins to loose strength at a much lower temperature than steel. Expect a 10% reduction at 400 degrees F solution temperature while steel the same loss is at 700 degrees F. 3. Annealed yield strength is usually 20,000 psi while steel is 30,000 psi. 4. COST! Expect 4 to 6 times the cost over steel depending upon construction content. I'm building a all copper boiler for a 1.6" scale NYC&HR 999 that is about 90% complete and have about $2,500 into it so far.

As I mentioned above I'm building an all copper 1.6" scale boiler. I have the outer shell complete along with the fire box with tubes and flues using girder crown stays. The outer shell is currently on the frame as all external attachments are sorted out. It is fabricated entirely out 1/4" thick copper plate. Construction techniques are a little more "serious" than those used for 3/32" o r 1/8" thick copper used in the smaller scales. If there is an interest I can do a few installments that will out line how I went about the construction. Like anything there is always more than one way to skin a cat. I don't claim my method is the best, just how I'm doing it.

Your copper boiler, how are you closing the seams? Silver braze, TIG.or what? Would love to see a few photos. I have finished and have had my boiler certified for a 1"scale loco. It is all silver brazed. Cost was about $800. This include the silver solder. The barrel is 5 inches in diameter and about 19 inches long.

$800 to $1000 for a 5" diameter boiler of about that size is where I budget a build -> is somewhat dependent on the dollar to sterling exchange rate since I get the shell and flues from Reeves in the UK.

daves1459 wrote: I'm building a all copper boiler for a 1.6" scale NYC&HR 999 that is about 90% complete and have about $2,500 into it so far.

As I mentioned above I'm building an all copper 1.6" scale boiler. I have the outer shell complete along with the fire box with tubes and flues using girder crown stays. The outer shell is currently on the frame as all external attachments are sorted out. It is fabricated entirely out 1/4" thick copper plate. Construction techniques are a little more "serious" than those used for 3/32" o r 1/8" thick copper used in the smaller scales. If there is an interest I can do a few installments that will out line how I went about the construction. Like anything there is always more than one way to skin a cat. I don't claim my method is the best, just how I'm doing it.

Daves1459,

Yes interested.... I've been welding copper for years but using a method that most (me included) do not have access to. I've been butt welding copper, full penetration in a vacuum chamber with an electron beam welder - a CNC welder in a 6' x 6' x 7' vacuum chamber. (I'm tempted to work some 'weekends' on a boiler.) There is no filler, the parts are fused together by the beam. The parts must fit very closely to control hot strength between parts. I, along with other EBW welders, are not so eager to weld copper because of its quick to a very watery liquid state when molten. It must be welded fast and hot because it can't given time to drop through - tricky!

TIG welding is planned for this boiler and the weld joints are of interest in how you did them. I've read and been informed that a welded 'T' butt is not a good method; but to use formed and radiused end sheets, throat sheets and etc. butt welded from both sides.....?? Butt welding the front flue sheet all the way to the front end inside the barrel looks like a problem....

Anyhow - yes; much interest. (I'm only up to about $1600 deep in copper for a boiler and bronze for bushings).

Maybe we should be nice to the OP and move this 'TIG copper boiler' discussion to another thread? What do you think Harold? With utmost respect and interest in the 'Coppersmithing A Boiler' discussion - which is similar but not.

BClemens wrote:Maybe we should be nice to the OP and move this 'TIG copper boiler' discussion to another thread? What do you think Harold? With utmost respect and interest in the 'Coppersmithing A Boiler' discussion - which is similar but not.

BC

Depends on if the OP is offended, or not. I tend to allow (even encourage) deviations from the original topic, assuming the discussion remains related, as that's how many learn what they hope to learn.

When splitting a thread, it's not always easy to make a clean separation, as the topic at hand may be referenced in posts that may be candidates to be moved. Not easy to resolve situations like that, so more damage than good can result.

If there is good reason to split this thread, I'll do it. Mean time, continue to toss out thoughts. No harm comes from sharing one's knowledge.

H

Wise people talk because they have something to say. Fools talk because they have to say something.

Please excuse the delay in answering the questions and moving forward on a series of installments on the construction of my boiler.

The copper heat exchanger weld test were simply test strips butt welded and lap joint welded then evaluated in a tensile test machine. After test the pieces were sectioned and examined. No complete heat exchangers were made and tested.

The seams of my copper boiler are closed with Safety-Silv 56. I used 1/4-20 silicon bronze screws to hold everything securely in place for silver brazing. I'll explain my spacing and procedures in the construction series.

Cost is a major consideration in boiler construction. The following is as complete a summary of material cost I can put together. The copper costs are actual and represent the best price I could find from Internet suppliers at the time in 2010. Those listed afterwards are from recollection. Because of cash flow restrictions purchases were made incrementally as construction progressed.

WOW! I didn't realize I had so much into this thing. What is not included is the countless hours in making dies, forming, machining, assembly, and brazing. I can hardly wait to get the opinions on this.

A friend of mine just lost the boiler on his Allen 10 wheeler after 22 years. He meticulously took care of it and it finally rusted through. He says Marty Knox estimated a replacement boiler at $4,200. ( Marty will have to confirm.) His and my boiler are approximately the same size. So for 22 +/-
years life, effort, and cost one has to ask if copper is a valid choice for a 1 1/2" scale medium size boiler. For me it has been a project of passion as I've built several steel boilers that had to be repaired eventually and I just wanted to try making one.